This invention relates to a diaphragm carburetor suitable for supplying fuel to an engine used as a power source for most handheld gasoline powered products. More particularly, the invention relates to devices and methods for allowing an inexpensive and effective means of electrical control of small engines offering functionality similar to that of auto engines.
Diaphragm carburetors are generally used to supply fuel to two-cycle engines. These carburetors are equipped with a fuel pressure regulator that ensures fuel fed from a fuel pump is regulated at a fixed pressure, and then delivered to an air intake path. The fuel pressure regulator is typically equipped with a constant-pressure fuel chamber that stores fuel sent from the fuel pump. The constant-pressure fuel chamber is generally separated from atmosphere by a diaphragm that adjusts the fuel pressure to a constant pressure. A control valve that is interlocked to the motion of the diaphragm opens and closes a fuel passageway through which fuel flows to the fuel chamber. Fuel from the fuel chamber is delivered to the air intake path via a main fuel path and an idle fuel path. The main fuel path leads to a main nozzle that is open to a venturi in the air intake path. The idle fuel path leads to slow and idle ports that open adjacent to a throttle valve in the air intake path.
Conventional diaphragm carburetors are pre-set at an equipment manufacturer""s assembly line to deliver fuel at a predetermined flow rate to an engine the carburetor is coupled to. Manufacturing tolerances in the size and location of fuel paths, and the stiffness of the diaphragms, require that the manufacturer individually adjust each carburetor to achieve a desired flow rate. After these adjustments are made, all fuel path adjustment needles are capped to prevent subsequent tampering. The equipment is then shipped all over the world, and often times the carburetors are never readjusted to accommodate for local environmental conditions, fuel type or engine load.
This standardized manufacturing approach can lead to inefficient engine performance. Local environmental conditions, such as temperature and altitude, as well as engine loading and fuel type used can effect engine performance. All of these factors have an effect on the amount of fuel required for an optimal fuel/air ratio. The typical carburetor does not adjust for these variables, and the result is an engine that operates at less than peak performance and has higher exhaust emissions levels.
For example, engines operated in cold weather require additional fuel. Cold conditions inhibit fuel vaporization and cold air is denser, requiring additional fuel to achieve the proper fuel/air ratio. At higher altitudes, the air is less dense, and less fuel is required to obtain the proper fuel/air ratio. Typically, carburetors are set for peak performance at full load. However, when engines are run at less than peak power, less fuel is required. Lastly, different regions throughout the country, and the world, have different environmentally driven requirements for the amount of oxygenates that are added to fuel. Currently, engines are adjusted for optimal performance using the most oxygen rich fuels. Thus, when less-oxygenated fuels are used, excess fuel is used. Other conditions, including periods of start-up, warm-up, acceleration and deceleration, may also contribute to engine inefficiencies that could be corrected by varying the fuel flow rate to the engine.
Manufacturers have attempted to address this problem by placing a solenoid valve in a fuel passage through which fuel flows to the constant-pressure fuel chamber of the carburetor. The valve can be fully opened or fully dosed in response to electronic feedback generated from engine performance indicators. The problem with this device is that the resultant fuel path is either fully open or fully closed with no intermediate positions available.
Thus, it would be desirable to provide much finer control of the position of the fuel control valve to enable more accurate control of fuel delivery to the engine without a significant increase in cost or complexity of the device.
The proposed device of the present invention tends to facilitate much finer position control of a carburetor fuel flow control valve. This advantageously tends to result in more accurate control of fuel delivery to the engine without a significant increase in cost or complexity of the device.
In an exemplary embodiment of the present invention, a magnet and wire coil assembly are coupled to a metering diaphragm of the carburetor""s fuel pressure regulator. The diaphragm, as with conventional diaphragm carburetors, contacts a lever that is connected to an inlet needle of a fuel control valve positioned in a passageway through which fuel flows to a constant pressure fuel chamber. Movement of the diaphragm controls the size of the opening of the control valve and, thus, fuel flow through the passageway to the constant-pressure fuel chamber. Preferably, the magnet is attached to the metering diaphragm and extends outside a bottom cover of the carburetor into the center of a wire coil that is attached to or is an integral part of the bottom cover.
Application of an electric current to the coil turns the coil into an electromagnet By controlling the direction and amount of current through the wire coil, the direction and degree to which the magnet travels can be controlled. Movement of the magnet, in turn, pushes or pulls the metering diaphragm inward and outward relative to the fuel chamber. In operation, the current flow through the coil is preferably modulated to provide either an inward bias or an outward bias on the diaphragm. An inward bias will cause the inlet needle to open further than normal and result in a greater amount of fuel being delivered to the engine. An outward bias will prevent the inlet needle from opening as far as normal and will result in less fuel being delivered to the engine. Thus, by controlling the current through the wire coil, one can control the amount of fuel flow through the carburetor and to the engine.
Electronic feedback generated from engine performance can be used to control the current input to the wire coil. In this way the engine will self-adjust so that the optimal fuel/air ratio will be achieved. This will result in lower exhaust emissions and improved engine performance.